1. Field of the Invention
The present invention relates to a secondary battery with charging and discharging capabilities, in particular to a photochargeable air battery that is discharged by oxidation and charged by light energy.
2. Relevant Art
Experiments that attempt to charge secondary batteries using the light energy of visible sunlight and the like have been conducted in the past. As this type of battery, photochargeable batteries are known which combine secondary batteries such as amorphous silicon solar cells, nickel-cadmium batteries and lead-acid batteries (J. Electrochem. Soc. Vol. 131, No. 9, pp. 2037-2041:1984). These photochargeable batteries will be explained with reference to FIGS. 21-22. FIG. 21 shows a perspective view of a prior art photochargeable battery, and FIG. 22 shows an equivalent circuit of the photochargeable battery in FIG. 21. The photochargeable battery shown in FIGS. 21 and 22 comprises a solar cell 1, a storage battery 2 which stores electrical power obtained by this solar cell 1, a voltage regulation circuit 3 which regulates the voltage generated in solar cell 1, and a check diode 4 which prevents flow of the electric current from storage battery 2 to solar cell 1. Photochargeable battery 2 functions in a two-step (indirect) process which comprises generation of electrical power using solar cell 1, and storage of the electrical power obtained by this solar cell 1 using storage battery 2.
However, this type of prior art photochargeable battery has disadvantages in that as a result of the required structural components of the voltage regulation circuit 3, check diode 4 and the like, the structure of this photochargeable battery is extremely bulky and complex.
As well, there exist additional problems in that in the proper functioning of the prior art photochargeable battery it is necessary to regulate the electric current appropriated for charging the electrical power generated by solar cell 1 to storage battery 2, and in order to perform this regulation a large amount of energy loss take place. In addition, the aforementioned photochargeable battery possesses, as a result of passing through a light.fwdarw.electric.fwdarw.electrochemical three-phase energy conversion step, problems such as an increase in the number of structural components for this energy conversion step, or an increase in the energy loss attributed to this energy conversion step.
Further disadvantages exist in the manufacturing of solar cell 1, as comparatively high grade manufacturing equipment such as p-n junction equipment is required, in addition to other difficulties outside of manufacturing.
FIG. 23 shows a prior art photochargeable battery (Kogyozairyo, 1989, No. 3, Vol. 7-4, pp. 18-22). This photochargeable battery is equipped with transparent glass substrate 7, P-type semiconductor 8, I-type semiconductor 9, collecting elements 10, 11, cathode 12, anode 13, solid electrolyte 14, passivation layer 15, and transparent electrode 16. However, as in the aforementioned, the construction of this photochargeable battery is complex and drawbacks exist such as problems in manufacturing the semiconductors as well as low energy density.
FIG. 24 shows a structural view of a prior art photochemical chargeable battery (Faraday Discuss. Chem. Soc. 70, pp. 207-222:1980). In the Fig. battery container 17, cover 17a for sealing tightly the battery container, separator 18, photo-electrode 19 formed from an N-type semiconductor, electrode 20a for charging, and electrode 20b for discharging are shown.
FIG. 25 shows a simple structure and energy level of a photochemical chargeable battery (Bull. Chem. Soc. Jpn., 56. pp. 2873-2876:1983) .
These photochemical chargeable batteries utilize an electrochemically distinct semiconductor-electrolyte, in particular, they utilize an energy band curve generated at the time of contact of semiconductor electrode with the electrolyte, and electrochemically accumulate this light energy. The photo-conversion portion of the photochemical chargeable battery shown in FIG. 24 is formed by simply dipping semiconductor electrode 19 into electrolyte S, and thus in regards to this point, it is superior when compared with prior art photochargeable batteries requiring solar batteries and the like as shown in FIGS. 21 and 22.
However, as shown in FIG. 25, in shifting from discharging to charging (or vice versa), there exist a drawback in that the electrode connection must be changed using a switch or the like. Thus, disadvantageous exist in that the reactions of these batteries are based on electrolytic reduction-oxidation reactions, and thus in order to increase capacity a large amount of electrolyte is required, and generally a large energy density is undesirable.